title: Analysis of nuclear actin by overexpression of wild-type and actin mutant proteins.
abstract: Compared to the cytoplasmic F-actin abundance in cells, nuclear F-actin levels are generally quite low. However, nuclear actin is present in certain cell types including oocytes and under certain cellular conditions including stress or serum stimulation. Currently, the architecture and polymerization status of nuclear actin networks has not been analyzed in great detail. In this study, we investigated the architecture and functions of such nuclear actin networks. We generated nuclear actin polymers by overexpression of actin proteins fused to a nuclear localization signal (NLS). Raising nuclear abundance of a NLS wild-type actin, we observed phalloidin- and LifeAct-positive actin bundles forming a nuclear cytoskeletal network consisting of curved F-actin. In contrast, a polymer-stabilizing actin mutant (NLS-G15S-actin) deficient in interacting with the actin-binding protein cofilin generated a nuclear actin network reminiscent of straight stress fiber-like microfilaments in the cytoplasm. We provide a first electron microscopic description of such nuclear actin polymers suggesting bundling of actin filaments. Employing different cell types from various species including neurons, we show that the morphology of and potential to generate nuclear actin are conserved. Finally, we demonstrate that nuclear actin affects cell function including morphology, serum response factor-mediated gene expression, and herpes simplex virus infection. Our data suggest that actin is able to form filamentous structures inside the nucleus, which share architectural and functional similarities with the cytoplasmic F-actin.
authors.affiliation: Institute for Physiological Chemistry, Ulm University, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
authors.forename: Enikö
authors.initials: E
authors.lastname: Kokai
authors.forename: Henning
authors.initials: H
authors.lastname: Beck
authors.forename: Julia
authors.initials: J
authors.lastname: Weissbach
authors.forename: Franziska
authors.initials: F
authors.lastname: Arnold
authors.forename: Daniela
authors.initials: D
authors.lastname: Sinske
authors.forename: Ulrike
authors.initials: U
authors.lastname: Sebert
authors.forename: Gerd
authors.initials: G
authors.lastname: Gaiselmann
authors.forename: Volker
authors.initials: V
authors.lastname: Schmidt
authors.forename: Paul
authors.initials: P
authors.lastname: Walther
authors.forename: Jan
authors.initials: J
authors.lastname: Münch
authors.forename: Guido
authors.initials: G
authors.lastname: Posern
authors.forename: Bernd
authors.initials: B
authors.lastname: Knöll
mesh_terms: D000199:Actins / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D007150:Immunohistochemistry; D050505:Mutant Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D000199:Actins; D050505:Mutant Proteins